In process automation technology, field devices are often used for the registering and/or influencing of process variables. Examples of such field devices are fill level measuring devices, mass flow measuring devices, pressure and temperature measuring devices, pH-redox potential measuring devices, conductivity measuring devices, etc, which, as sensors, register the corresponding process variables fill level, flow rate, pressure, temperature, pH-value and conductivity.
Besides such measuring devices, systems are also known, which, along with the measuring function, also perform other tasks; examples that can be named here are electrode cleaning systems, calibration systems, and sample takers.
Also referred to as field devices are input/output units, so-called remote I/Os.
Serving for the influencing of process variables are field devices referred to as actuators, e.g. valves, which control the flow rate of a liquid in a section of pipeline, or pumps, which influence fill level in a container.
The firm ENDRESS+HAUSER® manufactures and sells a large number of such field devices.
Field devices in modern manufacturing plants are frequently connected with superordinated units, e.g. control systems or control units, via a field bus system (PROFIBUS®, FOUNDATION®-fieldbus,HART®, etc.). These superordinated units serve for process control, process visualization, process monitoring, as well as for operating and monitoring of the field devices. From the superordinated units, communication connections to further company networks are also possible.
For operating field devices, corresponding operating programs (operating tools) are required in the control system, or in the control unit, as the case may be. These operating programs can run independently or they can be integrated into control-system applications.
The sensors deliver measured values corresponding to the current value of the registered process variable. These measured values are forwarded to a control unit, e.g. a PLC (programmable logic controller).
As a rule, process control occurs from the control unit, where the measured values of different field devices are evaluated and, on the basis of the evaluation, control signals for the corresponding actuators are produced. Besides pure, measured value transmission, field devices can also transmit additional information (diagnosis, status, etc.). Parametering and configuring of the field devices occurs, likewise, via the field bus system.
The field bus system is referred to also as the process control system.
Requirements for safety in process control systems are becoming ever stricter. Therefore, in many enterprises, process control systems are strictly separated from other company networks (SAP, business). In this way, unauthorized access to field devices is to be prevented. At the moment, efforts are being concentrated on safety in process control systems at the network level.
For preventing intrusions from outside the company, so-called firewalls are used. Besides intrusions from outside of the company, likewise dangerous are unauthorized intrusions from within a company. In the case of company-internal intrusions, e.g. parameters can be changed in the field devices, or the entire control strategy can be changed. This can lead to undesired changes in the production process.
A control strategy can be produced e.g. with the FieldCare® system of the firm Endress+Hauser and loaded into the field devices.
Programs, which enable parametering, configuring and a changing of the control strategy (SCADA-systems or configuration tools) are usually equipped with a password protection. In such case, also an authorizing of the personnel who perform changes is necessary.
For example, in the case of the CENTUM® CS 1000 process control system of Yokogawa, critical function blocks, which run e.g. in field devices, can only be changed via input of two pass words of different persons.
In the case of the firm Endress+Hauser, safety protection against unauthorized changing of parameters in field devices is provided by a locking. The person who wants to make changes must input a code at the field device, before changes in the field device become possible.
Field devices used in process control systems normally are equipped with microprocessors and accompanying peripheral components.
Therefore, it is not possible to exclude the possibility that hardware, or software, or even just parts thereof, might be replaced, or changed, in a field device without authorization. A tampering of this kind would not be recognized by a process control system. Yet, measures such as these represent a significant intrusion into the process flow, or control strategy. Especially also for reasons of laws and regulations, it is important for a plant operator that a tamper-safe process flow be assured.